TWI681940B - Silica glass member and method of manufacturing same - Google Patents

Abstract

Provided is a silica glass member which exhibits high optical transparency to vacuum ultraviolet light and has a low thermal expansion coefficient of 4.0 × 10^-7/K or less at near room temperature, particularly a silica glass member which is suitable as a photomask substrate to be used in a double patterning exposure process using an ArF excimer laser (193 nm) as a light source. The silica glass member is silica glass to be used in a photolithography process using vacuum ultraviolet light as a light source, in which the fluorine concentration is 1 wt% or more and 5 wt% or less, and the thermal expansion coefficient at from 20℃ to 50℃ is 4.0 × 10^-7/K or less.

Description

Silicon dioxide glass component and manufacturing method thereof

The invention relates to a silicon dioxide glass component and a manufacturing method thereof. In detail, the present invention relates to a silica glass member for a photomask that can be suitably used for lithography in the vacuum ultraviolet wavelength range.

In recent years, in the lithography technology, the requirements for miniaturization of semiconductor devices have increased day by day, and the use of liquid immersion exposure technology by shortening the exposure wavelength or immersing pure water between the lens and the wafer has increased The method of opening number of lens used for exposure.

Regarding the resolution R in photolithography, if the wavelength of the exposure light is λ, the number of openings representing the lens performance of the exposure device is NA, and the process constant is k1, then R=k1λ/NA The formula shows that if the exposure wavelength λ is shortened, the number of openings NA is increased, and the process constant k1 is reduced, the resolution can be improved.

Here, regarding the exposure wavelength λ, i-ray (365nm), KrF excimer laser (248nm), ArF excimer laser (193nm), and the short wavelength of the light source have been used since the g-ray (436nm) of the mercury lamp Transformation is being promoted.

The number of openings NA represents the size of the lens in the form of geometry. When the lens is used to focus the exposure light and imaged on the wafer surface, NA=n. The expression of sin θ (n represents the refractive index of the medium between the lens and the wafer, θ represents the opening angle of light).

Here, if ArF excimer laser with a wavelength of 193 nm for exposure light is used and the liquid immersion exposure technique is used, the resolution of 43 nm can be achieved when the number of openings is set to 1.35 and the process constant k1 (k1 factor) is 0.3 .

In addition, for the substrate for photolithography using the ArF excimer laser, in terms of low thermal expansion and excellent light transmittance, a silica glass substrate can be suitably used.

As the performance required for the silica glass substrate, when ArF excimer laser is used, light resistance that does not deteriorate the light transmittance even when exposed to high-energy light can be cited. In addition, in the case of liquid immersion exposure, since the difference between the refractive index of the pure water existing between the lens and the wafer and the refractive index of the resist becomes small, the opening angle of the light increases, and the polarization effect becomes a problem. Therefore, the silica glass substrate needs to have low birefringence. The reason why low birefringence is required is that if the silica glass substrate has birefringence, polarization of the exposure light transmitted through may sometimes change and the imaging performance may deteriorate.

For example, in Japanese Patent Laid-Open No. 2001-180963 (Patent Document 1), as a method of manufacturing silica glass that satisfies these requirements, the following method has been disclosed: flame hydrolysis is performed by making a silica glass forming raw material While making porous II VAD (Vapour-Phase Axial Deposition; Vapor Axial Deposition) method is used to make silica glass ingot after oxidizing silica glass body (smoke particles), and then heat-treated in hydrogen atmosphere to dope OH group with hydrogen. This improves the light resistance to ArF excimer lasers and the like.

In addition, Japanese Patent Laid-Open No. 2002-316831 (Patent Document 2) discloses a method for manufacturing fluorinated silica glass, which is produced by flame hydrolysis of glass raw materials forming silica glass After the porous silica glass body (smoke particles) is subjected to dehydration, fluorine addition, and transparency treatment, the transmittance or laser resistance of vacuum ultraviolet light with strong energy such as F ₂ excimer laser is improved. Regarding the fluorine-added silica glass described in Patent Document 2, it is considered that by fluorine doping, the thermal expansion around room temperature is reduced by about 10% compared to the case of only quartz glass.

In addition, Japanese Patent No. 3228676 (Patent Document 3) discloses the following method: after the porous silica glass body (smoke particles) is melted at a vacuum degree of 100 Pa or less to produce a transparent glass, The fictive temperature setting process is performed in an atmosphere containing oxygen-containing gas or hydrogen-containing gas, thereby maintaining excellent transmittance at a wavelength of 165 nm even after irradiation with far ultraviolet rays.

On the other hand, as a method for modifying silica glass, for example, Japanese Patent Laid-Open No. 2006-225249 (Patent Document 4) discloses the following method: after manufacturing silica glass, annealing is performed under specific conditions The treatment is an additional treatment, thereby promoting the relaxation of the glass structure and reducing the birefringence. By changing part of the annealing treatment step to a hydrogen atmosphere, hydrogen doping is performed to improve the light resistance.

In order to achieve a resolution below 43 nm by the exposure method using ArF excimer laser, a double patterning method must be used. The so-called double patterning is a method of performing exposure in two. If this method is used, a resolution of 32 nm or less as a finer element pattern can also be achieved.

In the case of using double patterning to miniaturize the device, if the exposure cannot be performed with high precision at the position of the target pattern, a pattern shift will occur, so extremely high pattern registration accuracy is required between the two lithography .

Therefore, for the silica glass substrate for photomasks, in order to avoid positional shift caused by thermal expansion during exposure, a lower thermal expansion is required compared to the previous silica glass. Here, the overlap accuracy of the double patterned exposure refers to the total of the overlap accuracy of the two exposures, and the overlap accuracy required for each exposure can be said to be about 3 nm to 4 nm. On the other hand, the thermal expansion coefficient of the usual silica glass is 5.0×10 ^-7 /K to 6.0×10 ^-7 /K, and the 1cm quartz piece stretches 5nm to 6nm as the temperature of 1K rises, so accuracy is required It is difficult to say sufficient. Therefore, the thermal expansion of silica glass substrates for photomasks is required to be less than that of conventional silica glass.

In addition, as a silica glass substrate for a light-transmitting photomask, the exposure wavelength of ArF excimer laser, that is, the light transmittance of 193 nm is required to be equal to that of the previous silica glass.

About silica glass characterized by low thermal expansion, known as ULE (Ultra-Low Expansion; Ultra Low Expansion) glass (Corning Code 7972) of Corning, etc. (<Amorphous Materials)>>, in Paper presented to the Third International Conference on the Physics of Non-Crystalline Solids held at Sheffield University, September, 1970 (non-patent literature) 1)). In Non-Patent Document 1, it has been reported that TiO _{2 is} doped into silica glass to reduce thermal expansion, and by adjusting the TiO ₂ concentration, it exhibits extremely low thermal expansion of 0.1×10 ⁻⁷ /K or less. However, the absorption end of the TiO ₂ -SiO ₂ glass-based ultraviolet wavelength exists between 300 nm and 400 nm, so the light transmission of 193 nm is extremely poor, and it cannot combine both low thermal expansion and light transmission (<<Amorphous Solid Journal (Journal of Non-Crystalline Solids)>>, vol.11 (1973), p.368 (Non-Patent Document 2)). The reason for the above situation is that by doping TiO ₂ , absorption is generated in the visible light range due to so-called dd migration between energy gaps in the d electronic structure of Ti. In addition, it is known that the absorption in the visible light range obtained by Ti ions is affected by adjacent oxygen atoms. It is known that the absorption wavelengths are different due to the valence of ions of Ti ³⁺ and Ti ⁴⁺ , but they all absorb between 300 nm and 400 nm. band. Therefore, it is required to develop a silica glass substrate obtained by a method other than TiO ₂ -SiO ₂ based glass.

The object of the present invention is to provide a silica glass member having high light transmittance of vacuum ultraviolet light and lower thermal expansion than the previous silica glass, and a manufacturing method thereof.

The silica glass component of the present invention is a silica glass used in the photolithography step using vacuum ultraviolet light as a light source, and is characterized in that the fluorine concentration is 1 wt% or more and 5 wt% or less, and 20°C to 50°C The coefficient of thermal expansion is 4.0×10 ^-7 /K or less.

The silica glass member of the present invention has the above-mentioned structure, ArF excimer laser (193 nm) has high light transmittance, and thermal expansion is lower than that of the previous silica glass.

The density of the aforementioned silica glass member is preferably 2.16 g/cm ³ or more and 2.19 g/cm ³ or less.

The aforementioned silica glass member preferably has an OH group concentration of 10 ppm or less.

The virtual temperature of the aforementioned silica glass member is preferably 1000°C or lower.

Preferably, the concentration of Fe, Cr, Ni, Cu, and Ti in the aforementioned silica glass member is 1 wtppm or less, and the viscosity rate at a temperature of 1000° C. is 10 ^14.5 dPa. s below.

The aforementioned silica glass member preferably has a linear transmittance of 90% or more for light having a wavelength of 193 nm.

The manufacturing method of the silica glass component of the present invention is characterized by preparing silica glass with a fluorine concentration of 1 wt% or more and 5 wt% or less, and using a heating furnace to treat the silica glass at a temperature of more than 1000°C and a viscosity ratio of 10 ^14.5 dPa. After the temperature below s to 1500 ℃ heating, take out from the heating furnace and quenching treatment (quick cooling), again at 400 ℃ to 1000 ℃ below and the viscosity of silica glass becomes 10 ^14.5 dPa. Annealing is performed within the temperature range below s.

According to the present invention, an ArF excimer laser (193 nm) can provide a fluorine-doped silicon dioxide glass member with high light transmittance and lower thermal expansion than the previous silicon dioxide glass and a manufacturing method thereof.

The silica glass component of the present invention is, for example, a porous silica body (smoke particles) doped with fluorine and transparentized, and then quenched from a temperature above 1000°C and then below 1000°C Annealing treatment is performed within the temperature range to achieve low thermal expansion of 4.0×10 ^-7 /K or less near room temperature.

Such a silica glass member is suitable as a reticle substrate used in a double-pattern exposure step using ArF excimer laser as a light source.

FIG. 1 shows the transmittance curve of Example 1. FIG.

The silicon dioxide glass component of the present invention is a silicon dioxide glass used in the photolithography step using vacuum ultraviolet light as the light source, and the fluorine concentration is 1 wt% or more and 5 wt% or less, and the coefficient of thermal expansion of 20°C to 50°C is 4.0×10 ^-7 /K or less.

Hereinafter, the above-mentioned configuration conditions of the present invention will be described in detail.

In the present invention, the fluorine concentration in the silica glass member is 1 wt% or more and 5 wt% or less. Fluorine-doped silica glass exhibits low thermal expansion at temperatures above 300°C. This is well known in previous studies of fluorine-doped optical fibers, and the thermal expansion coefficient at 400°C is reported to be 2.5×10 ^-7 /K(<<Fiber Development of optical fibers in Japan>>, New York: Gordon and Breach Science Publishers (c1989). However, even if it is such a fluorine-doped silica glass, the thermal expansion coefficient is hardly affected between 20°C and 50°C including room temperature. For example, the thermal expansion coefficient of 5℃ to 65℃ of silica glass doped with 1.5wt% of fluorine is almost unchanged compared with that without fluorine (<<Research Report Asahi Glass Co. , Ltd.) >>, 57 (2007)).

In terms of principle, the doped fluorine is replaced with the OH group as the terminal structure of silica glass, and part of the member ring structure (such as three member ring structure, four member ring structure, six member ring structure, etc.) is cut off The new end group structure is produced, so depending on the doping conditions, it can sometimes be doped with other end groups (such as OH group, Cl group, etc.) contained in the silica glass by more than 10 times in weight ratio Of fluorine. Moreover, silica glass with a large number of end-group structures has the characteristic of becoming low viscosity.

The so-called low viscosity means that the silica glass has a low density and undergoes structural changes at a relatively low temperature. Moreover, the low viscosity also means that the molecules in silica glass have high fluidity at high temperature, and the structural change becomes obvious. That is, the temperature range of the silica dioxide glass structure with a large number of end group structures varies widely. So much By combining quenching treatment and annealing treatment with a large amount of fluorine-based silica glass, setting of a virtual temperature in a wide temperature range becomes easy and the density can be controlled.

In the present invention, the silicon dioxide glass is doped with fluorine, and a predetermined heat treatment is applied, thereby obtaining a fluorine concentration of 1 wt% or more and 5 wt% or less, which is reduced in density and has a coefficient of thermal expansion of 20×50°C of 4.0×10 ^-7 Silicon dioxide glass components below K.

Specifically, the above-mentioned silica glass member can be manufactured by, for example, a so-called VAD method in which a silica silica glass-forming raw material is subjected to flame hydrolysis to form a porous silica body (smoke particles) and then subjected to transparency treatment (Japan Patent Publication No. 2001-342027). That is, after forming soot particles, it is treated in a mixed gas atmosphere in which an inert gas such as helium is mixed with SiF ₄ gas, whereby after doping with fluorine, it is transparentized in a fluorine-containing atmosphere (mixed gas atmosphere), and A predetermined heat treatment is carried out, thereby manufacturing a silica glass member.

The fluorine concentration in the mixed gas (the concentration ratio of SiF ₄ gas) is preferably more than 5 vol% to 35 vol%, more preferably 10 vol% to 35 vol%, and particularly preferably 25 vol% to 35 vol%. In addition, the introduction temperature of the mixed gas is preferably 1000°C to 1300°C, more preferably 1100°C to 1200°C. If the introduction temperature is lower than 1000°C, the diffusion of fluorine into the glass structure may be slow, and the doping may not be sufficient. On the other hand, if it exceeds 1300°C, the smoke particles may start to sinter, and the diffusion of fluorine into the glass structure may be hindered.

In the present invention, for example, by adjusting the concentration ratio of SiF ₄ gas in the mixed gas and the calcination temperature in the transparency process, the fluorine concentration in the obtained silica glass member is set to 1 wt% or more and 5 wt% or less .

The so-called predetermined heat treatment in the present invention is a step of quenching the fluorine-doped silica glass above 1000°C after the transparency treatment, and then performing the annealing treatment below 1000°C. In addition, the quenching treatment can also be continued without cooling temporarily after the aforementioned transparency treatment.

The quenching treatment in the present invention refers to heating the silica glass to a temperature range of 1000°C to 1500°C, and the viscosity ratio becomes 10 ^14.5 dPa. s or less, preferably 10 ^13.0 dPa. Below s, then the silica glass is rapidly cooled to below 800℃. For the temperature after rapid cooling, 600℃ is better than 800℃, 400℃ is better than 600℃, the lower the better. In addition, regarding the cooling rate, rapid cooling of about 1000K is required in about 1 second. For example, rapid cooling can be mentioned as follows: moving directly from the heating furnace to a low-temperature refrigerant such as an adjacent gas or liquid. For example, it is only necessary to perform the following treatment: heat the silica glass to 1500°C, and then release it into the atmosphere to spray air, or dive the silica glass into a pure water pool. At this time, as long as the air flow rate after being put into the atmosphere is set to a value sufficient for cooling, or the volume of a pure water pool sufficient for the target silica glass is prepared based on the heat capacity calculation, the dioxide can be The temperature of the silica glass is rapidly cooled to the temperature of the refrigerant.

In addition, because quenching treatment requires instant cooling as much as possible, it is preferable to make the silica glass into a thin plate shape for quenching treatment compared to the bulk shape. In addition, it can also be performed in air, but more preferably in water Or oil and other liquids. In particular, large-scale silica glass can be thinned in advance in order to cool the silica glass uniformly and rapidly. In the present invention, the viscosity of silica glass is mainly determined by the amount of fluorine and temperature, but by heating until the viscosity is sufficiently reduced, the silica glass is rapidly cooled to cool the characteristics of the silica glass before cooling Fixed, reduce the thermal expansion rate at room temperature. Specifically, the viscosity ratio through silica glass becomes 10 ^14.5 dPa. The temperature of s is rapidly cooled from a temperature higher than 200°C to a temperature lower than 100°C, which can achieve the low thermal expansion rate for the purpose of the invention.

If fluorine is added, the silica glass becomes low-viscosity, so it is speculated that the molecular vibration in the glass above 1000°C is large, and the volume expansion occurs microscopically. When the quenching treatment is performed in this state, the glass structure is frozen and the density is reduced while maintaining the volume expansion state.

However, sometimes the local strain caused by the small-member ring structure represented by the 3-member ring or the 4-member ring due to the quenching process remains in the structure. In this case, annealing treatment to remove the strain after the quenching process is required. Annealing treatment must be below 1000 ℃ and the viscosity rate should be 10 ^14.5 dPa. Within the range below s. The annealing temperature is determined by the temperature characteristics of silica glass. For example, since the strain point of silica glass with a fluorine concentration of 1 wt% or more and 5 wt% or less is 1000°C or less, the annealing temperature is usually 1000°C or less, preferably 800°C or less, and more preferably 600°C to 400°C Perform annealing. After rapid cooling by quenching treatment, the cooled silica glass is heated with a heater or the like, for example, an annealing treatment is performed at a temperature of 400°C for 50 hours, whereby the silica glass can maintain a low density state And eliminate local strain. If the temperature is lower than 400℃, the effect of annealing treatment is not ideal.

Furthermore, the so-called strain point means 10 ^14.5 dPa. The temperature of the viscosity ratio of s is actually the temperature that can cause the viscous flow of silica glass, which is equivalent to the lower limit temperature in the slow cooling area. Therefore, the viscosity ratio of the silicon dioxide glass member of the present invention at 1000°C is preferably 10 ^14.5 dPa. Below s, more preferably 10 ^13.0 dPa. s below.

The coefficient of thermal expansion of the silica glass member thus obtained at 20°C to 50°C is 4.0×10 ^-7 /K or less, preferably 3.2×10 ^-7 /K or less, and more preferably 3.0×10 ^-7 /K the following. In addition, the density of the aforementioned silica glass member at 20°C to 50°C is 2.16 g/cm ³ or more and 2.19 g/cm ³ or less, specifically 2.190 g/cm ³ or less, preferably 2.185 g/cm ³ or less , more preferably 2.16g / cm ³ or more 2.180g / cm ³ or less. If the density is less than 2.16 g/cm ³ , the surface hardness of the silica glass member tends to be insufficient, and sometimes it is damaged during the grinding step or the transportation step, and it cannot be used for the photolithography step. Furthermore, the density of the silica glass component is also related to the fluorine concentration, so the fluorine concentration is 1 wt% or more and 5 wt% or less, preferably 1.5 wt% or more and 5 wt% or less, and more preferably 3 wt% or more and 5 wt% or less.

It is known that the thermal expansion of silica glass varies depending on the virtual temperature (<Journal of Non-Crystalline Solids>>, vol. 5 (1970), p. 123). The so-called virtual temperature refers to the temperature corresponding to the temperature at which the freezing occurs in the glass where the structure in the supercooled liquid state at high temperature is frozen. It is known that silicon dioxide glass also differs in thermal expansion depending on the density, and there have been reports of increased thermal expansion coefficients of high-density glass systems ("Materials", Volume 32, No. 362, p.64). That is, the structure of silicon dioxide glass is different depending on the density or freezing temperature. For example, in the case of high-density glass, the gap between the glass network structures, called the free volume, becomes smaller, and molecular vibrations that accompany the temperature increase will occur. The relaxation gap is small, so the volume expansion becomes obvious.

It is known that the virtual temperature can be changed by annealing silicon dioxide glass. The virtual temperature also depends on the OH group concentration in the silica glass. The more the OH group concentration, the easier the virtual temperature decreases. The reason for the above situation is that the OH group exists at the end of the glass structure, and the ring structure is cut due to the annealing process, the fluidity of the glass structure is improved, and the temperature at which the structure freezes becomes lower. However, there is a limit to changing the virtual temperature of silica glass to reduce the density. The thermal expansion coefficient of silica glass that changes the virtual temperature and the concentration of OH groups is approximately 6.0×10 ^- from 20°C to 400°C- Report from ⁷ /K to 6.5×10 ^-7 /K (<Journal of Non-Crystalline Solids>>, vol.355(2009), p.323).

On the other hand, it has been previously known that if fluorine is doped in silica glass, the member ring structure is cut and the glass structure changes. For example, there have been reports of changes in the junction angle of the -Si-O-Si- bond of the member ring structure (<Journal of the Ceramic Society of Japan>>, vol.120(2012), p.447). That is, by doping fluorine in the silica glass, the virtual temperature can be changed, and the density of the silica glass can be reduced.

In the present invention, the glass having a fluorine group can control the virtual temperature by combining quenching treatment and annealing treatment, but in order to set the thermal expansion coefficient of 20°C to 50°C to 4.0×10 ^-7 /K or less, the virtual temperature is preferably Below 1000°C, more preferably below 900°C. When the virtual temperature exceeds 1000°C, most of the silica glass is in a state where local strain is not eliminated. In this case, it may sometimes fail to exhibit stable low thermal expansion. Furthermore, the virtual temperature can be obtained based on the calculation formula reported in the Journal of Non-Crystalline Solids (vol. 185 (1995), p. 191). It is known that the virtual temperature is related to the infrared absorption wave number of the asymmetric stretching vibration of Si-O-Si in silica glass, and it is expected that the vibration number will be changed by doping fluorine in the glass structure. If the glass with known fluorine concentration is heat-treated at a predetermined temperature in advance, the temperature is regarded as a virtual temperature, and the difference from the value calculated by the basic formula is used as a correction factor, the virtual temperature of the fluorine-doped glass can be calculated. Several reports of these calculation formulas are known. In the present invention, the formula used when the fluorine concentration reported in Patent Document 2 is 1 wt% or more is used.

In the silica glass member of the present invention, the OH group concentration is preferably 10 ppm or less. When the OH group concentration exceeds 10 ppm, it may be difficult to set the fluorine concentration to 1 wt% or more. The reason for the above is that the fluorine and OH groups are exchanged, so there is a trade-off relationship between the higher the OH group concentration and the lower the fluorine concentration.

It is preferable that the concentration of Fe, Cr, Ni, Cu, and Ti contained in the silica glass member obtained in this way is 1wtppm or less, respectively, and the viscosity ratio at a temperature of 1000°C is 10 ^14.5 dPa. s below.

In order to use a silica glass member in the photolithography step using an ArF excimer laser light source, light transmission at an exposure wavelength of 193 nm is required. At this time, the metal impurities in the glass cause the deterioration of the permeability. Especially as transition metals such as Fe, Cr, Metal impurities represented by Ni, Cu, and Ti cause d-d migration between d orbitals as the excitation level of electrons, and have absorption ends in the visible light range, so that the transparency in the ultraviolet range is significantly deteriorated. Therefore, as mentioned above, the concentration of these metal impurities is preferably 1 wtppm or less in the silica glass member.

The above-mentioned silica glass member can be used for photolithography using vacuum ultraviolet light as a light source. Here, the vacuum ultraviolet light refers to electromagnetic waves having a wavelength in the vicinity of 10 nm to 200 nm, and the vacuum ultraviolet laser includes ArF excimer laser (193 nm) or F ₂ laser (157 nm).

Regarding the light transmittance of the ArF excimer laser at the exposure wavelength of 193 nm in the above-mentioned silica glass member, the linear transmittance is 85% or more, preferably 90% or more, and more preferably 91% or more, which is the same as the previous dioxide The light transmittance of silica glass is equal to or higher.

[Example]

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the examples shown below.

[Example 1]

SiCl ₄ as a glass forming raw material was hydrolyzed in an oxyhydrogen flame, and the generated silicon dioxide fine particles were deposited on palladium made of quartz glass to obtain porous silicon dioxide (smoke particles) having a diameter of 200 mm and a length of 500 mm. Then, the aforementioned smoke particles were put into the furnace, and the temperature was changed to SiF ₄ 20vol% + He 80vol% after heating to 1200°C at a heating rate of 400°C/h in a helium atmosphere at a flow rate of 20 L/min. The mixed gas (flow rate 15L/min) was kept at 1200°C for 3 hours for fluorine doping treatment.

After the fluorine-doping treatment was completed, the atmosphere was maintained as it was, and the temperature was raised to 1400°C at a heating rate of 400°C/h, and the transparent treatment was performed at 1400°C for 2 hours to obtain a silica glass ingot having a diameter of 120 mm and a length of 230 mm.

After returning the ingot to room temperature for a while and cutting it to make a thin plate with a thickness of 6.4mm, the thin plate was put into an electric furnace and heated in an atmospheric atmosphere. After holding at 1100°C for 1 hour, it was taken out from the furnace body and sprayed with a large amount The air is quenched by rapid cooling to 20°C. Furthermore, after the quenching treatment, it was reheated to 1000°C again at a temperature increase rate of 100°C/h in the atmosphere and allowed to stand to cool naturally, thereby performing annealing treatment to obtain a silica glass member.

After the obtained silica glass member was cut and processed into a cylindrical shape, thermal expansion measurement was performed using a light interference type thermal expansion meter (LIFA-2). Further, a short strip sample of 20 mm×40 mm×6.4 mm was cut out, and after optical polishing, the linear transmittance at a wavelength of 193 nm was measured using a vacuum ultraviolet measuring device (JASCOVUV-200), and the virtual temperature was measured using an infrared spectroscopic measuring device (Nicolet 6700) , And the OH concentration obtained from the OH absorption peak. And F concentration analysis by ion chromatography, density measurement by Archimedes method (JIS (Japanese Industrial Standards) R1634), metal impurity analysis by mass analyzer, beam bending Method (ISO (International Organization for Standardization; International Organization for Standardization) 7884-4) to measure the viscosity rate.

[Example 2]

In the embodiment example 1, the ratio of SiF ₄ 30vol% with a mixed gas of He is set to: 70vol% of fluorine-doped, except that, in the same manner as in Example 1 to obtain silicon dioxide glass member. Then, the same test and evaluation as in Example 1 were performed.

[Example 3, Example 4]

In Example 1, a doping treatment in which the ratio of SiF ₄ to He mixed gas was 30 vol%: 70 vol% was performed, and the resulting thin plate was quenched at 1300°C for 1 hour and then at 800°C (Example 3) A silicon dioxide glass member was obtained in the same manner as in Example 1 except that annealing was performed at 600°C (Example 4). Then, the same test and evaluation as in Example 1 were performed.

[Example 5]

In Example 1, the silicon dioxide glass member was obtained in the same manner as in Example 1 except that a fluorine-doping treatment in which the ratio of SiF ₄ to He mixed gas was 8 vol%: 92 vol% was performed. Then, the same test and evaluation as in Example 1 were performed.

[Example 6]

In Example 1, a fluorine-doped treatment in which the ratio of SiF ₄ to He mixed gas was set to 8 vol%: 92 vol%, and after quenching, the thin plate was annealed at 800° C. Except for this, it was the same as in Example 1. The silica glass member was obtained in the same manner. Then, the same test and evaluation as in Example 1 were performed.

[Example 7]

In Example 1, a silica glass member was obtained in the same manner as in Example 1 except that the thin plate was dropped from the furnace body and immersed in water at normal temperature during the quenching process. Then, the same test and evaluation as in Example 1 were performed.

[Example 8]

The smoke particles produced in the same manner as in Example 1 were placed in a furnace, and the temperature was changed to SiF in a helium atmosphere at a flow rate of 20 L/min at a heating rate of 400°C/h to 1200°C. ₄ 25 vol% + He 75 vol% mixed gas (flow rate 15L/min), kept at 1200 ℃ for 3 hours for fluorine doping.

After the above-mentioned fluorine doping treatment is completed, the atmosphere is set to a mixed gas of SiF _{4 20} vol% + He 80 vol%, and the temperature is raised to 1400°C at a heating rate of 400°C/h, and then kept transparent at 1400°C for 2 hours to obtain a diameter of 120 mm. , Silica glass ingot with a length of 230mm.

After the thin plate (thickness 6.4mm) made of the obtained silica glass ingot was kept in the atmosphere at 1300°C for 1 hour, the silica glass ingot was dropped from the furnace body, immersed in water at normal temperature for quenching treatment . Furthermore, after the quenching treatment, it was heated again to 600°C at a temperature increase rate of 100°C/h in the atmosphere, and allowed to stand and cool naturally, thereby performing annealing treatment to obtain a silica glass member.

[Example 9]

The smoke pellets produced in the same manner as in Example 1 were put into the furnace, and the temperature was changed to SiF ₄ after heating up to 1200°C at a heating rate of 400°C/h in a helium atmosphere with a flow rate of 20 L/min. The mixed gas of 35vol%+He 65vol% (flow rate 15L/min) is kept at 1200℃ for 3 hours for fluorine doping.

After the above-mentioned fluorine doping treatment is completed, the atmosphere is set to a mixed gas of SiF _{4 20} vol% + He 80 vol%, and the temperature is raised to 1400°C at a heating rate of 400°C/h, and then kept transparent at 1400°C for 2 hours to obtain a diameter of 120 mm. , Silica glass ingot with a length of 230mm.

The obtained silicon dioxide glass ingot was slowly cooled and maintained at 1300°C for 1 hour, and then fell from the furnace body and immersed in water at normal temperature, thereby performing quenching treatment. Furthermore, after the quenching treatment, the temperature was again increased to 400° C. at a heating rate of 100° C./h in the atmosphere, and it was left to cool naturally, thereby performing annealing treatment to obtain a silica glass member.

[Comparative Example 1]

In Example 1, a fluorine-containing treatment in which the ratio of SiF ₄ to He mixed gas was set to 5 vol% and 95 vol% was carried out, and in the same manner as in Example 1, silica glass was obtained. Then, the same test and evaluation as in Example 1 were performed.

[Comparative Example 2, Comparative Example 3]

In Comparative Example 1, the sheet was kept at 1300°C for 1 hour and then quenched, and annealed at 1000°C (Comparative Example 2) and 800°C (Comparative Example 3). In the same manner as in Comparative Example 1, silica glass was obtained. Then, the same test and evaluation as in Example 1 were performed.

[Comparative Example 4]

In Example 1, the silicon dioxide glass member was obtained like Example 1 except the quenching process was omitted. Then, the same test and evaluation as in Example 1 were performed.

[Comparative Example 5]

In Example 1, the silicon dioxide glass member was obtained like Example 1 except that the annealing process was omitted. Then, the same test and evaluation as in Example 1 were performed.

[Comparative Example 6]

In Example 1, the quenching process and the annealing process were omitted, and the silica glass member was obtained in the same manner as in Example 1. Then, the same test and evaluation as in Example 1 were performed.

Table 1 shows the results of Examples 1 to 9 and Comparative Examples 1 to 6. In addition, the transmittance curve of Example 1 is shown in FIG. 1.

In the embodiments, the silica glass is described as being obtained by hydrolysis using a oxyhydrogen flame, but the silica glass can also be manufactured by other methods. For example, silica glass obtained by adding fluorine and obtained by the sol-gel method may be quenched, and then Heat treatment.

(Industry availability)

The silica glass member of the present invention can be suitably used for light lithography using vacuum ultraviolet light such as ArF excimer laser (193 nm) or F ₂ laser (157 nm) as a light source.

Claims (6)

A silica glass component, which is a silica glass used in the photolithography step using vacuum ultraviolet light as a light source, and has a Ti concentration of 1 wtppm or less, an OH group concentration of 10 ppm or less, and a fluorine concentration of 1 wt% or more and 5 wt % Or less, and the coefficient of thermal expansion from 20°C to 50°C is 4.0×10 ^-7 /K or less. The silica glass member according to claim 1, wherein the density is 2.16 g/cm ³ or more and 2.19 g/cm ³ or less. The silica glass member according to claim 1 or 2, wherein the virtual temperature is 1000°C or lower. The silica glass member as described in claim 1 or 2, wherein the concentrations of Fe, Cr, Ni and Cu are each 1wtppm or less, and the viscosity at a temperature of 1000°C is 10 ^14.5 dPa. s below. The silica glass member according to claim 1 or 2, wherein the linear transmittance of light with a wavelength of 193 nm is 90% or more. A manufacturing method of low thermal expansion silica glass is to prepare silica glass with a Ti concentration of 1wtppm or less, an OH group concentration of 10ppm or less, and a fluorine concentration of 1wt% or more and 5wt% or less, using a heating furnace to have a viscosity of 10 ^14.5 dPa. After heating the silica glass in the temperature range from 1000℃ to 1500℃, taking it out of the heating furnace and performing quenching treatment, that is, rapid cooling, the viscosity of silica glass becomes 10 ^14.5 dPa again. The method below s is annealed in the temperature range of 400°C or more and 1000°C or less.

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